Air conditioning apparatus having sterilization function

ABSTRACT

This air conditioning apparatus having sterilization function which can maintain the sterilization function for a long time period. The air conditioning apparatus having a sterilization function comprises a sterilizing coating layer formed on the surface of a component, wherein the sterilizing coating layer has copper or copper alloy particles dispersed in a resin matrix. The coating layer is formed by dispersing fine copper or copper alloy particles having a maximum particle size of about 2.5 μm or less into an epoxy or epoxy-acryl synthetic resin, and covered on the surface of a component of the air conditioning apparatus such as a heat exchanger. The maximum content of the copper or copper alloy particles in the coating layer is preferably about 18 to 31 wt %. The thickness of the coating layer is preferably less than the maximum size of the particle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air conditioning apparatus having a sterilization function and a method for a producing sterilizing material for use in the air conditioning apparatus.

2. Description of the Related Art

Sources of microorganism exist in various types. Fungi or bacteria exist in substantially all air conditioning apparatus if they provide nutrients and satisfy temperature and humidity requirements. The air conditioning apparatus for feeding fresh air to residential environments provide habitats to fungi and bacteria resulting from temperature and humidity characteristics of components (for example, high humidity in the surface of a cooling coil), improper management and etc., and thus pollute indoor air. Hereinafter, we will exemplify those components of the air conditioning apparatus which allow existence and growth of microorganism:

Filter: A filter is installed in an air conditioning apparatus to filtrate dust from the open air or during ventilation. The quantity of dust stuck to the filter (possessed dust) increases as time lapses. It has been reported that microorganism such as Penicillium inhabits dust which is stuck to the filter. When the filter captures dust exceeding its possessing ability or abrupt turbulence occurs to the pressure within the air conditioning apparatus during running it, microorganism stuck to the filter is scattered on dust, which is heaped up and stuck on the surface of a downstream coil, the inside surface of a humidifier and the inside surface of a duct and is discharged to the atmosphere of a room. Further habitation and growth of microorganism stuck to the filter clogs up holes of the filter, thereby lowering filtering ability, degrading performance and shortening lifetime.

Coil Surface: Since the open air has a high fungus concentration or the filter has a low capturing ability, a large quantity of microorganism permeates a downstream side of the filter and thus sticks to the surface of a cooling coil. The surface of the cooling coil allows growth of microorganism since it is hot and contains dust attachment functioning as nutrients for microorganism.

Humidifier: It is becoming evident that microorganism inhabits a humidifier, in particular, the interior of a humidifier using water, which has temperature and humidity conditions adequate for growth of microorganism and contains dust which is heaped and stuck thereon.

Duct Interior: It is also being confirmed that microorganism exists within a duct. The quantity of dust heaped and stuck inside the duct increases in proportion to used time period of the duct. Further, the inside of the duct has a relatively higher humidity during cooling and thus provides an amicable environment to microorganism.

Bleeder Surface: Particles in a bleeded air flow collide against a bleeder and stick thereon and a portion of air flow is induced adjacent to the bleeder so that particles contained in the air flow stick on the bleeder. As a result, the bleeder surface is polluted in proportion to elapsed time. It is also found that microorganism such as Aspergillus inhabits the bleeder surface.

Others: It is known that microorganism also exists in various places such as an acoustic absorbent, a heat insulator, a plenum, a drain pan and a cooling tower in addition to the above components. The heat insulator built in the air conditioning apparatus and the acoustic absorbent (e.g., a sound chamber, an elbow and a bleeder box) for absorbing sound in a duct unit used for saving energy or absorbing sound are made of dehumidifying material. If surfaces of the heat insulator and the acoustic absorbent are soiled, they provide environments which promote growth of microorganism so that microorganism thrives therein. Further, microorganism grows in the ceiling plenum since the open air penetrates through a small gap of the ceiling plenum and the temperature and humidity of the ceiling plenum is not regulated. If the drain pan is wetted by drain water, it is exposed to the air so that microorganism grows therein. Furthermore, the cooling tower used for cooling water is reported as a habitat of microorganism which causes Legionella and Pontiac fever.

Considering the foregoing background, it is required to devise antibacterial or sterilizing ability to components of an air conditioning apparatus. For example, there are proposed technologies in which heat exchanger fins are made of copper, the fins are coated with a layer containing copper or an ultraviolet lamp is installed to sterilize directly components (as disclosed in Japanese Laid-Open Patent Publication H12-97447; Hereinafter it will be referred to as “reference cited”).

The reference cited has sufficient sterilizing ability since it is designed to use pure copper. However, there is a problem in that it is difficult to maintain the sterilizing ability for a long time period. That is, copper ions are discharged from the copper layer to destruct cell membranes of microorganisms, thereby obtaining the sterilizing ability of copper. However, pure copper forms an oxide layer on its surface so that the quantity of copper ions decreases in proportion of elapsed time. As a result, pure copper may rarely maintain its sterilizing ability for a long time period.

Further, even though the fins are made of copper as in the reference cited, copper is rarely discharged since only a small surface area of the fins contribute to discharge, which is also undesirable in maintaining the sterilizing ability for a long time period.

Furthermore, in formation of a copper-containing coating layer on the surface of a component of the air conditioning apparatus, coating copper-containing material on the surface of an aluminum piece of a component material before performing mechanical process such as cutting or bending to the aluminum piece to form a component member is preferred to coating a previously shaped component member. However, simple coating has problems in that the coating layer may be peeled off or bonding force may be reduced in mechanical treatments after coating.

In particular, in a component of the air conditioning apparatus such as a heat exchanger which requires heat conduction in the component member itself, the copper-containing coating layer may insulate heat conduction, thereby degrading heat conductivity.

Furthermore, there are industrial problems in that pure copper is expensive and fabrication is not simple even though the fins are made of copper or coated with copper-containing material.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems and it is therefore a main object of the present invention to provide an air conditioning apparatus capable of maintaining sterilizing effects for a long period of time.

Another objects of the present invention are to increase the bonding force of a coating layer, inhibit degradation of heat conductivity by the coating layer and produce simply and economically.

In order to accomplish these objects of the invention, according to one aspect of the present invention, there is provided an air conditioning apparatus having a sterilization function, comprising a surface covered with a sterilizing coating layer, which has copper or copper alloy particles dispersed in a resin matrix (claim 1).

The invention as mentioned above is characterized in that it makes use of particles of copper or copper alloy, and that a coating layer containing the particles dispersed in a resin matrix is coated on a surface of the components of the air conditioning apparatus. Herein, the term “copper alloy” is alloy of copper and zinc. Zinc has a sterilizing capability equal to that of copper. Moreover, it is difficult for copper alloy to cause surface oxidation, so that unlike pure copper, copper alloy is vulnerable to ion elution, which is prevented by an oxide film. Additionally, since the particles of copper alloy have a large surface area, their ions can be easily eluted. As a result, the present invention can maintain long-term treatment effects of sterilization.

Further, since copper alloy is harder than copper, copper alloy is easily formed into particles and is cost-effective. Therefore, the present invention has an advantage in that the air conditioning apparatus can be easily produced at a low cost.

In the present invention, the term “component surface” does not mean to distinguish inside of the component from outside. In other words, there is no limitation to whether the surface is exposed outside the component or inside. Therefore, it simply means that it is not an interior of a material of which the component is made. For example, in the present invention, the “component surface” includes both inner and outer surfaces of each fin of a heat exchanger.

Meanwhile, according to another aspect of the present invention, there is provided an air conditioning apparatus having sterilization function, wherein the particles of copper or copper alloy contained in the coating layer is fine powder having a maximum diameter of about 2.5 μm or less, and the content of the particles in the layer is about 13 to 51 wt % (claim 2).

In this manner, when the fine powder of copper or copper alloy is mixed at the ratio, the particles of copper or copper alloy is well dispersed in the resin matrix, so that the coating layer is formed to uniformly exert a sufficiently sterilizing characteristic.

Further, according to yet another aspect of the present invention, there is provided an air conditioning apparatus having sterilization function, wherein the coating layer is formed on at least one member which require heat conduction at a thickness of about 2 μm or less (claim 3).

When the fine powder of copper or copper alloy of claim 2 is used together with the ratio as mentioned above, and when the coating layer is formed at the thickness of claim 3, the coating layer is formed not only to uniformly exert a sufficiently sterilizing characteristic, but also to maintain heat conductivity.

According to yet still another aspect of the present invention, there is provided an air conditioning apparatus having sterilization function, wherein the coating layer has a thickness less than the maximum diameter of the particles of copper or copper alloy (claim 4).

In this manner, when the coating layer has a thickness less than the maximum diameter of the particles of copper or copper alloy, some particles of copper or copper alloy are exposed outside the coating layer, so that the sterilizing effect is well maintained.

According to yet still another aspect of the present invention, there is provided an air conditioning apparatus having sterilization function, which further comprises. The pretreated layer is interposed between the coating layer and the component surface in order to enhance bonding strength of the coating layer (claim 5).

Thus, the pretreatment layer allows the bonding strength between the coating layer and the component surface to be enhanced, so that it is possible to provide an easy and efficient production method to coat on components prior to mechanical processing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view illustrating a sterilizing coating layer according to the invention;

FIG. 2 is a conceptual view of a sterilizing coating system;

FIG. 3 is a graph of experimental results; and

FIG. 4 is a graph of experimental results.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description will present a preferred embodiment of the invention in reference to the accompanying drawings.

FIG. 1 is a sectional view of an air conditioning apparatus having sterilizing coating layers according to the invention. In FIG. 1, the reference number 1 designates a section of an important component such as heat exchanger fins in the air conditioning apparatus, which is covered with sterilizing coating layers 2 having copper or copper alloy particles dispersed in resin matrix. While the coating layers 2 may be formed on a portion of the component, it may be preferred that the coating layers 2 are formed on regions of the component as wide as possible. The coating layers 2 may be preferably formed, for example, on entire inner and outer surfaces of heat exchanger pins.

In the present invention, the copper or copper alloy particles preferably have a maximum particle size of about 2.5 μm or less, and more particularly, in a range of about 2.0 to 2.5 μm, in view of improvement of sterilizing ability owing to increase of surface area, dispersability with respect to a resin matrix and fine producibility.

The coating layers 2 of the invention preferably contain the copper or copper alloy particles of about 13 to 51 wt %, and more preferably, about 18 to 31 wt %. Where the content of copper or copper alloy exceeds about 51 wt %, the volume ratio of copper or copper alloy is raised, which may potentially lower the bonding strength of resin while worsening the dispersability of the copper particles. Where the content of copper or copper alloy does not reach about 13 wt %, sterilizing ability is not sufficient. It is more preferable that the content of copper or copper alloy ranges from about 18 to 31 wt % since the above problems can be more effectively overcome in this range. The range of about 13 to 51 wt % corresponds to the copper or copper alloy particles occupying about 5 to 20 wt % with respect to a coating composition, and the range of about 18 to 31 wt % corresponds to the copper or copper alloy particles occupying about 7 to 12 wt % with respect to the coating composition. The coating composition contains xylen, diacetone alcohol, cyclohexane and so on functioning as an auxiliary solvent for forming final coating layers. These substances are volatilized and thus not found in the final coating layers.

Available examples of the resin matrix of the invention may include thermosetting resins such as epoxy resin, epoxy-acryl synthetic resin, polyester resin and phenol resin; thermoplastic resins such as polyamide resin, polycarbonate resin, polypropylene resin and polyvinyl chloride resin; known paint matrix and etc.

A suitable resin of several characteristics such as heat conductivity, absorptance and strength may be selected according to the use of the air conditioning apparatus. For example, epoxy resin and epoxy-acryl synthetic resin are adequate since they have a large value of heat conductivity (which is typically adequate to a heat exchanger and so on), a small value of absorptance (which prevents swelling and peeling), a high strength (which prevents peeling), inexpensive cost and so on. Further, the coating layers 2 of the invention may contain for example pigment under 6%.

The coating layers 2 preferably have a thickness of about 2 μm or less, and more preferably, about 1.5 to 2.0 μm in order to improve heat conductivity. Since the coating layers 2 contain the copper or copper alloy particles excellent in heat conductivity, the coating layers 2 in the above thickness range substantially do not cause heat conductivity degradation.

According to the above description, the coating layers 2 may satisfy all of dispersability with respect to the resin matrix, fine producibility and heat conductivity by determining the copper or copper alloy particles as fine powder having a maximum particle size of about 2.5 μm or less and the copper layer thickness to about 1.5 to 2.0 μm.

The air conditioning apparatus of the invention may form the sterilizing coating layers 2 directly on the component surface. Since peeling off the sterilizing coating layers 2 may ruin the purpose of the invention, it is more preferably recommended and promoted to form pretreatment layers (or primer layers) 3 on the component surface for facilitating bonding of the sterilizing coating layers 2 to the component surface before formation of the sterilizing coating layers 2. The pretreatment layers 3 may be formed using a known pretreatment paint for example based upon chromium oxide, preferably, to a thickness of about 0.5 μm or less.

While the coating layers 2 may be formed for example via spray coating after fabrication of the air conditioning apparatus of the invention, such spray coating, etc. is not adequate in a complex structure such as the heat exchanger fins. As a result, it is most preferred to form the sterilizing coating layers 2 before machining a member of the air conditioning apparatus. FIG. 2 illustrates an equipment 10 for forming the sterilizing coating layers on the member of the air conditioning apparatus.

Describing the construction of the equipment 10 in more detail, a strip S1 made of aluminum for example is sequentially unwound from a coil C1, and transported to a first coating unit 11. The first coating unit 11 sequentially coats a pretreatment solution on both surfaces of upper and lower portions of the strip S1. After coated with the pretreatment solution, the strip S1 undergoes firing (heating) in a painting furnace 12 and cooling in a cooling furnace 13 to be converted into a strip S2 formed with pretreatment layers. The strip S2 is transported into a second coating unit 14.

The second coating unit 14 melts the copper or copper alloy particles and a resin matrix solution into a suitable solvent (such as xylene and diacetone alcohol). A sterilizing coating solution added with pigment if necessary is coated on the pretreatment layers on both surfaces of the upper and lower portions of the strip S2. In the event of using a coating solution which is formed previously, the coating solution is preferably stirred at least before being coated in order to prevent precipitation of copper or copper alloy particles. The strip coated with the sterilizing coating solution undergoes firing in a painting furnace 15 and cooling in a cooling furnace 16 to be converted into a strip S3 to which the sterilizing coating layers are strongly bonded. The strip S3 is recovered, wound into a coil C2. Layer thickness-measuring units 17 (such as based upon far infrared ray absorptivity) are preferably arranged, respectively, downstream of the coating units 11 and 14 to measure the thickness of the pretreatment layers and the sterilizing coating layers in order to manage the thickness of the layers.

After sterilizing coating is completed through the above processes, the strip S2 is shaped into members through mechanical treatment such as cutting and bending, and then the members are assembled to fabricate the air conditioning apparatus of the invention.

In the invention, the term “air conditioning apparatus” refers to those instruments constituting the air conditioning apparatus, in particular, an instrument allowing passage of air, a heat exchanger such as a coil or fin, a duct, a drain fan and a lower water tank of a cooling tower. Further, the invention may provide sterilizing coating treatment together with a sterilizing means such as an ultraviolet lamp.

Effects of the invention will be described through the following examples.

Confirmatory Experiment of Sterilizing Ability

Several samples were prepared from aluminum pieces as reported in Table 1, in which samples 1 to 5 (inventive example) were coated with copper or copper alloy particles according to the invention, sample 6 (comparative example) did not undergo sterilization coating, sample 7 (inventive example) replaced copper alloy particles of the first example by pure copper powder, and sample 8 (comparative example) was made of a pure copper plate. Other conditions which are not described in Table 1 are commonly applied to all of the samples. Copper alloy particles contain copper and zinc which are alloyed in the ratio of 8 to 2. TABLE 1 No. 1 2 3 4 5 6 7 8 9 Coating Epoxy 30 28 26 30 31 — 30 — 30 Xylen 32 30 28 32 33 — 32 — 32 Diacetone 19 18 16 19 19 — 19 — 19 alcohol Cyclohexane 11 11 9 11 11 — 11 — 11 Sterilizing 7.0 12 20 7.0 5 — 7.0 — 7.0 Particle¹⁾ (18) (31) (51) (18) (13) (18) (18) Pigment 1.0 1.0 1.0 1.0 1.0 — 1.0 — 1.0 Pretreatment Chromium 3.0 3.0 3.0 3.0 3.0 — 3.0 — 3.0 Solution trioxide (wt %) Phosphoric 1.0 1.0 1.0 1.0 1.0 — 1.0 — 1.0 acid Formaldehyde 0.5 0.5 0.5 0.5 0.5 — 0.5 — 0.5 Solvent 95.5 95.5 95.5 95.5 95.5 — 95.5 — 95.5 Maximum Diameter(μm) 2 2 2 5 2 — 2 — 1.5 Coating Thickness(μm) 1.5 1.5 1.5 4.5 1.5 — 1.5 — 2 Sterilizing Particles ²⁾ ²⁾ ²⁾ ²⁾ ²⁾ Al Pure Cu ²⁾ plate Cu plate Note 1: Values in brackets indicate the content of the particles (measured values) in final coating layers. Note 2: Copper Alloy Particle

Two test strains including E. coli and Staphylococcus aureus are provided, and standard strains were enriched and cultured at about 35±1° C. for about 24±2 hours in a typical Bouillon culture medium up to a population of about 5 to 10×10⁵ CFU/ml in a sterilizing phosphoric acid buffer solution to form a solution of standard strains. The samples were softly cleaned two or three times with gauze or absorbent cotton wetted with ethanol, and then dried in the air.

The samples were inoculated with the standard strain solutions of about 0.5 ml in sterilized Petri plates, and then maintained at a temperature of about 37±1° C. and a relative humidity of about 90% or more for 8, 18 and 24 hours. As a comparison sample, 0.5 ml standard strain solutions were inoculated into sterilized Petri plates, which were maintained at a temperature of about 37±1° C. and a relative humidity of about 90% or more for 0, 8, 18 and 24 hours.

After predetermined time periods, the samples and controls were sufficiently washed with 9.5 ml SCDLP culture medium in the Petri plates (i.e., diluted up to about 20 times), and the washed solutions were cultured in standard agar medium at a temperature of about 35±1° C. for about 24±3 hours via Plate Count Agar (PCA). Then, numbers of bacteria were counted.

FIGS. 3 and 4 are graphs showing variation in numbers of bacteria, in which FIG. 3 shows results obtained from E. coli, and FIG. 4 shows results obtained from Staphylococcus aureus.

The results proved that the samples 1 through 5 of the invention show remarkable sterilizing ability over the aluminum plates. The samples 1 through 5 showed excellent sterilizing ability equal to or higher than those of the samples made of pure copper powder or copper plate. In the graph of FIG. 4, bacteria are increased, even though at a slight amount, in the samples made of pure copper powder or the copper plate after 18 hours. However, the samples 1 through 3 of the invention do not show increase of bacteria at all, and thus have excellent durability of sterilizing ability. The results also proved that sterilizing ability is improved up to 7 wt % of the copper or copper alloy particles in the coating solution (i.e., 18 wt % of the copper or copper alloy particles in the coating layer) but remains substantially steady exceeding 7 wt %. Further, sterilizing ability weakens slightly if the maximum particle size increases.

The sample 9 has a coating layer thickness larger than the maximum particle size of the copper alloy particles. When the sterilizing ability of the sample 9 was measured as above, it was found that the sterilizing ability of the sample 9 was slightly higher than that of the aluminum plate (i.e., sample 6) to which no treatment was performed. Therefore, it is understood that the coating layer thickness should be smaller than the maximum particle size of the copper alloy particles to exert fine sterilizing ability. This result is not shown in the drawings.

Confirmatory Experiment of Bonding Strength

Aluminum plates (samples 10 to 13) were prepared through sterilization coating same as that of above Confirmatory Experiment of Sterilizing Ability Sterilization. Then, the aluminum plates were tested with bonding ability and bending performance according to KS M 5400 (i.e., test method of paint and associated raw material). Types of the aluminum plates and experimental results are reported in Table 2. Bonding strength was tested with a checker pattern which has 100 crossings of notches and a pitch of 1 mm. Bending test was performed with a solid rod having a diameter of 2 mm and an auxiliary plate having a thickness of 4 mm. Further, other conditions which are not reported in Table 2 were applied in common to all of the examples. Sterilizing particles utilized in common copper alloy particles in which copper and zinc are alloyed in the ratio of 8 to 2. TABLE 2 No. 9 10 11 12 13 Coating Epoxy 30 30 30 30 30 Solution Xylen 32 32 32 32 32 (wt %) Diacetone 19 19 19 19 19 alcohol Cyclohexane 11 11 11 11 11 Sterilizing 7.0 7.0 7.0 7.0 7.0 Particle¹⁾ (18) (18) (18) (18) (18) Pigment 1.0 1.0 1.0 1.0 1.0 Pretreatment Chromium 3.0 3.0 3.0 3.0 — Solution trioxide (wt %) Phosphoric 1.0 1.0 1.0 1.0 — acid Formaldehyde 0.5 0.5 0.5 0.5 — Solvent 95.5 95.5 95.5 95.5 — Maximum Diameter (μm) 2 2.5 3 5 2 Coating Thickness (μm) 2 2 2 2 2 Bonding ability 10 10 9 8 5 Bending performance Endurable Endurable Sometimes Sometimes Sometimes peeling peeling peeling Note 1: Values in brackets indicate the contents of particles (measured values) in final coating layers.

From results in Table 2, it can be understood that bonding ability and bending performance are degraded where copper or copper alloy particles have a maximum particle size exceeding 2.5 μn and formation of a pretreatment layer is essential for a strong sterilizing coating layer.

Heat Conductivity Test

Aluminum plates were coated equal to the first example except that the coating layers have thicknesses of 2.5, 3, 4 and 5 μm. The aluminum plates of this example and the first example were tested with heat conductivity. In an air conditioning apparatus, the performance according to heat conductivity is expressed by cooling and heating capacities. Cooling and heating capacities were measured according to Annex 1 of KS C 9306 (Air Conditioner), entitled “Method of Measuring Cooling Capacity and Heating Capacity of Heat Pump.” Experimental results are reported in Table 3. TABLE 3 Coating Thickness (μm) 2 (1st Example) 2.5 3 4 5 Cooling Capacity (%) 100 99.8 99.5 98.3 97.6 Heating Capacity (%) 100 99.7 99.3 98.8 98.4

As can be seen from the above results, heat conductivity is excellent at a thickness of 2 μm, gradually drops at 2.5 μm, and remarkably drops from 3 μm. Therefore, it is most preferred that the coating layer has a thickness of 2 μm or less.

According to the present invention as set forth above, sterilizing effects can be maintained for a long time period.

The air conditioning apparatus of the invention can increase bonding force of a coating layer, inhibit degradation of heat conductivity by the coating layer and be produced simply and economically. 

1. An air conditioning apparatus having sterilization function comprising a sterilizing coating layer formed on the surface of a component of the air conditioning apparatus, wherein the sterilizing coating layer has copper or copper alloy particles dispersed in a resin matrix.
 2. The air conditioning apparatus according to claim 1, wherein the particles of copper or copper alloy contained in the coating layer are fine powder particles having a maximum diameter of about 2.5 μm or less, and the content of the particles in the layer is about 13 to 51 wt %.
 3. The air conditioning apparatus according to claim 2, wherein the coating layer is formed on at least one member which require heat conduction at a thickness of about 2 μm or less.
 4. The air conditioning apparatus according to claim 1, wherein the coating layer has a thickness less than the maximum diameter of the particles of copper or copper alloy.
 5. The air conditioning apparatus according to claim 2, wherein the coating layer has a thickness less than the maximum diameter of the particles of copper or copper alloy.
 6. The air conditioning apparatus according to claim 3, wherein the coating layer has a thickness less than the maximum diameter of the particles of copper or copper alloy.
 7. The air conditioning apparatus according to claim 1, wherein a pretreatment layer is interposed between the coating layer and the component surface to enhance the bonding strength of the coating layer.
 8. The air conditioning apparatus according to claim 2, wherein a pretreatment layer is interposed between the coating layer and the component surface to enhance the bonding strength of the coating layer.
 9. The air conditioning apparatus according to claim 3, wherein a pretreatment layer is interposed between the coating layer and the component surface to enhance the bonding strength of the coating layer. 